THE FOKM-EELATIONS OF THE HUMAN BRAIN. 



197 



then accompanies the margin of the hemisphere still farther; curves with 

 it into the temporal lobe, and ends only at its apex. 



The horizontal mass of transversely-divided fibers above the fornix 

 belongs to the corpus callosum. On this there is distinguished anteriorly 

 the genu, posteriorly the splenium, and between the two the hody. Between 

 the corpxis callosum and the fornix lies the triangular field of the septum. 

 Moreover, just in front of and below the fornix the eommissura anterior is 

 seen in transverse section; it lies in the middle of the lamina terminalis. 

 The lamina terminalis then continues ventrally into the floor of the inter- 

 brain, and is here somewhat infolded by the chiasma — also cut transversely. 



Fig. 133. — Longitudinal section through the middle of an adult brain. The 

 posterior portion of the thalamus, the crura cerebri, etc., have been removed, in 

 order to expose the inner surface of the temporal lobe. 



These structures, in part membranous, have been purposely left intact in 

 the preparation in order that the floor of the middle ventricle might be 

 seen once more. The posterior wall — the infundibulum and its transition 

 into the ventral region of the midbrain, the prominence of the tegmentum — 

 has also been left in place. In your own preparations, however, remove all of 

 these gray parts and observe how the fornix terminates behind the region 

 designated as uncus. 



The portion of the wall of the hemisphere which lies above the corpus 

 callosum is traversed by few and rather constant fissures. 



First of all, the sulcus cinguli runs parallel with the corpus callosum. 



